Dental Radiology Lecture- Chapter 5 & 6

exposure to chronic low levels of radiation have shown….

• no adverse biological affects (no bad changes)

• however, we are unable to predict a specific outcome from any amount of radiation exposure

2 theories of biological effect

• direct

• indirect

direct

• direct damage to cells

• 1/3 of alterations from x-ray exposure results from a direct effect

• ionizing radiation hits critical areas within the cell, causing damage

• good news!- most dental x-ray photons pass through a cell with little or no damage

indirect

• causes damage to water in the cell, potential to harm cell after

• strong tendency to recombine (high potential for recovery)

• radiolysis of water

• based on the assumption that radiation can cause chemical damage to cells by ionizing the water within it- forming free radicals

• free radicals form toxins (hydrogen peroxide) causing cellular dysfunction

• good news!- when water is broken down, there is strong tendency to recombine

ALARA concept

• as low as reasonably achievable

sequence of events following radiation exposure:

• latent period

• period of injury

• recovery period

latent period

• nothing shows then shows symptoms

• may be short or long, depending on initial dose

• SHORT-TERM- within minutes, days, or weeks

• LONG-TERM- within years, decades, or generations

period of injury

• actual injury to cell- cell division stops

• effects most often seen from radiation is the stoppage of mitosis (cell division)

• temorary or permanent

recovery period

• repair happens- usually naturally

• repair period; most injuries from low-dose radiation are repaired naturally

5 outcomes following radiation exposure:

• nothing happens

• cellular injury

• cell death

• damage to cell

• biophicial change

nothing happens

• cell is unaffected

cellular injury

• cell is injured or damaged but repairs itself function normally

cell death

• cell dies but is replaced through normal biological processes

damage to cells

• cell is injured or damaged

• repairs itself

• but now function at a reduced level

biophicial change

• cancer/tumor

• cell is injured or damaged and repairs itself incorrectly or abnormally, resulting in a tumor or malignancy

factors determining radiation

• total dose

• dose rate

• area exposed

• variation among species

• individual sensitivity

• variation in cells and tissue

• age

total dose

• type energy, and duration

• (greater the dose = more severe biological effect)

dose rate

• rate at which radiation is administered determines what effects will occur

area exposed

• larger the area, greater the injury (dental radiographs use a small beam, limiting the area of radiation exposure)

variation among species

• lethal doses for plants and m/o are 100’s of times higher than for mammals

• animals can take more than us

individual sensitivity

• individuals vary in sensitivity within the same species

• ex. red heads, cancer patients, autoimmune patients

variation in cells and tissue

• all cells and tissues are not equally sensitive to radiation

• lead apron- protect reproductive cells, thyroid

age

• younger cells are more susceptible to damage

• children are more susceptible than adults at the same dose

• increases again w the elderly

high sensitivity cells

• immature cells

  • embryo or fetus, immature reproductive cells

• quickly dividing cells

  • WBC’s

• younger persons cells

less sensitivity cells

• highly specialized cells

  • mature nerve cells

• mature cells

  • bone, cartilage, muscle

• slowly dividing cells

  • scar tissue

dose response curves

• radiation does can be placed on a graph to illustrate the probability of tissue response damage

dose response curves: 2 variables

• response

• dose

threshold dose-response curve

• no change to cells

• indicates there is a “threshold” amount of radiation below which no biological response would be expected

  • erythema is a “response”

nonthreshold dose-response curve

• what we go by

• any amount has potential to cause a biological response

  • the assumption that any amount of radiation exposure may produce damage is the basis for radiation safety conrol practices

somatic cells

• any cell of body that’s not reproductive

somatic effect

• occurs when biological change/damage occurs in the individual, but has not passed along to offspring

genetic cells

• you don’t get damage

• offspring does

• (lead apron to protect)

genetic effect

• describes changes in hereditary tissues that do not show in the individual, but show in the offspring

how do we decide to acquire images while protecting the patient

• clinical judgment

• dentist is the one prescribing x-rays

patient radiation protection measure: list them

• professional judgement

• technical ability

• technical standards

• equipment standards

• optimum film processing

professional judgement

• evidence based selection criteria

technical ability

• communication, knowledge of quality radiographs, continuing education

technical standards

• intraoral technique choice

• exposure factors (kVp, mA, time)

equipment standards

• filtration

• collimation

• PID length

• digital sensors/holders

• lead apron

protection measures for us: list them

• time

• shielding

• distance

time

• reduce exposure

shielding

• walls/lead apron

distance

• at least 6 feet away

• 45 degrees to the primary beam- due to scatter radiation

maximum permissible dose (MPD)

• the dose equivalent of ionizing radiation that is not expected to cause detectable body damage to average persons at any time during their lifetime

• set lower than believed the human body can safely accept

how much radiation can they take: radiation workers

• 5 rem/year

• does not apply to minors or pregnant workers

how much radiation can they take: general public

• lower than .5 rem/year

• 1/10 the dose permitted for radiation workers